1. Field of the Invention
The present invention relates to a printing apparatus using a vibration driven linear motor to feed a carriage.
2. Related Background Art
As a printing apparatus using a vibration driven motor, hitherto, there is a thermal jet type (refer to U.S. Pat. Nos. 4,723,129 and 4,740,796) as shown in FIG. 16. According to such a printing apparatus, an ink tank 12 is put on a carriage 4, an ink is spouted out from a printer head 13, and the ink is printed onto a sheet fed from a platen roller 14. In the printing apparatus, as a drive source to linearly feed the carriage 4, there is used a vibration driven motor of the type such that a vibrator 1 rectilinearly moves on a rail-shaped stator 8 by means as shown in JP-A-H3-93481.
A printing apparatus as shown in FIG. 17 has also been proposed in order to improve a sheet feeding precision and to make a thickness of the printing apparatus thin. Reference numerals 2 and 3 denote vibrators to feed a sheet. A sheet 16 is sandwiched by two vibrators 2 and 3 with a proper pressing force as shown in FIG. 17. A progressive bending vibration is formed in each of the vibrators 2 and 3. A spatial phase difference between those travelling waves is set to 180.degree.. Due to this, the bending vibrations of the vibrators 2 and 3 progress in a manner such that the convex portions always face the sheet 16 side. When an attention is paid to a mass point 2a of, for instance, a convex portion of the surface of each of the vibrators 2 and 3, the mass point 2a performs an elliptic motion. For instance, in FIG. 18, when an attention is paid to the vibrator 2, in the case where the travelling wave moves to the right as shown by an arrow 26, the mass point 2a performs a clockwise elliptic motion as shown in the diagram. Therefore, the moving direction of the mass point 2a of the convex portion of each of the vibrators 2 and 3 is opposite to the travelling direction of the vibration and such a motion acts as a transfer force to transfer the sheet 16. Although the vibrators 2 and 3 have two straight portions, since the directions of the transfer forces of the two straight portions are opposite, the sheet is fed by using the straight portion of one side. In the printing apparatus of FIG. 17, the sheet 16 is fed in the direction shown by an arrow in the diagram and is printed.
In the printing apparatus of the type such that the sheet is fed by the platen roller 14 as shown in FIG. 16, an electromagnetic motor to rotate the platen roller 14 is coupled with a feed roller in the paper feed mode and the sheet is automatically fed (not shown). However, the printing apparatus to feed the sheet by using the vibration driven motor as shown in FIG. 17 doesn't have an automatic document feeder.
In such a printing apparatus, the sheet cannot be also fed up to the end. That is, even when up to an arc portion of the vibrator is used to drive, a drive force in the arc portion is directed in the direction shown by an arrow in FIG. 19. Therefore, the sheet 16 can be fed up to an A portion and the sheet is sandwiched by two vibrators and is not delivered.
In the printing apparatus of the ink jet type, further, a recovering operation to suck out the ink is needed before printing so that the ink is not choked. In the printing apparatus of FIG. 16, such a recovering operation is performed by using the electromagnetic motor to rotate the platen roller 14 (not shown). However, the printing apparatus of FIG. 17 cannot perform such a recovering operation.